A conventional laundry treating apparatus includes a cabinet for defining an exterior appearance, a tub mounted in the cabinet, a drum rotatably mounted in the tub to wash laundry and a motor having a shaft fixedly coupled to the drum via the tub to rotate the drum.
The tub is supported in the cabinet by a spring and a damper. Such a spring connects an internal upper portion of the cabinet and an upper portion of the tub with each other and such a damper connects an internal bottom of the cabinet and a lower portion of the tub with each other.
Especially, the damper is coupled to both lower portions of the tub by a hinge, to absorb the vibration transferred to the tub when the drum is rotating.
More specifically, the damper includes a cylinder coupled to both lower portions of the tub by a hinge, and a cylindrical piston connected to the bottom of the cabinet by a hinge in a state of being movable in the cylinder, and a damping pad attached to an outer circumferential surface of the piston to generate friction against an inner circumferential surface of the cylinder.
However, even with the damper, such the conventional laundry treating apparatus has a limited ability of reducing vibration.
In other words, the conventional laundry treating apparatus has the motor fixedly coupled to a rear surface of the tub and the motor has the shaft that passes through the rear surface of the tub in a state of being supported by a bearing fixed to the tub. Accordingly, in the structure of the conventional laundry treating apparatus, the vibration generated by the rotating drum and the motor is transferred to the tub. Even though reduced by the damper and the spring, the vibration transferred to the tub might be transferred to the cabinet. In addition, the vibration of the tub caused by the rotating drum and the vibration of the cabinet might increase disadvantageously in case the drum is rotated in an unbalanced state that a dynamic balance is lost.
The dynamic balance, namely, dynamic equilibrium means a state that a centrifugal force or a moment created by a centrifugal force is zero with respect to a shaft, when a body of rotation rotates. When having a uniform mass distribution, a rigid body keeps dynamic balance.
Accordingly, it can be understood that a dynamic balance of a laundry treating apparatus is kept when mass distribution of laundry with respect to a shaft of a drum is in an allowable range (when the drum is rotated with vibrating within an allowable vibration range).
In contrast, a state that a dynamic balance is lost, in other words, unbalance means that mass distribution with respect to a shaft of a drum is not uniform when the drum is rotating. Such an unbalance state is caused when the laundry is not distributed in the drum uniformly.